Electroluminescent devices incorporating mixed metal organic complexes

ABSTRACT

An electroluminescent device in which there is an electroluminescent which comprises a complex of general formula (L α ) n M 1 M 2  or of general formula (L α ) n  M 1 M 2  (L p ), where L p  is a neutral ligand and where M 1  is a rare earth, transition metal, lanthamide or an actimide, M 2  is a non rare earth metal, L α is an organic complex and n is the combined valence state of M 1  and M 2 .

The present invention relates to electroluminescent devicesincorporating mixed metal complexes of transition metals and othermetals.

Materials which emit light when an electric current is passed throughthem are well known and used in a wide range of display applications.Liquid crystal devices and devices which are based on inorganicsemiconductor systems are widely used, however these suffer from thedisadvantages of high energy consumption, high cost of manufacture, lowquantum efficiency and the inability to make flat panel displays.

Organic polymers have been proposed as useful in electroluminescentdevices, but it is not possible to obtain pure colours, they areexpensive to make and have a relatively low efficiency.

Another compound which has been proposed is aluminium quinolate, butthis requires dopants to be used to obtain a range of colours and has arelatively low efficiency.

Patent application WO98/58037 describes a range of lanthanide complexeswhich can be used in electroluminescent devices which have improvedproperties and give better results. Patent Applications PCT/GB98/01773,PCT/GB99/03619, PCT/GB99/04030, PCT/GB99/04024, PCT/GB99/04028,PCT/GB00/00268 describe electroluminescent complexes, structures anddevices using rare earth chelates.

Hitherto electroluminescent metal complexes have been based on a rareearth, transition metal, lanthanide or an actinide or have beenquinolates such as aluminium quinolate.

We have now invented new electroluminescent metal complexes whichinclude a rare earth, transition metal, lanthanide or an actinide and anon rare earth, transition metal, lanthanide or an actinide.

According to the invention there is provided an electroluminescentdevice which incorporates a layer of an electroluminescent complex ofgeneral formula (_(ααα))_(n)M₁M₂ where M₁ is a rare earth, transitionmetal, lanthanide or an actinide, M₂ is a non rare earth metal, L_(α)isan organic complex and n is the combined valence state of M₁ and M₂.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1–9 show exemplary ligands L_(α) and Lp as described in thisapplication.

FIGS. 10 and 11 show exemplary quinolates and other electrontransmitting materials as described in this application.

FIGS. 12–16 show exemplary hole transmitting materials as described inthis application.

FIG. 17 is a diagrammatic section of an exemplary LED cell as describedin this application.

FIG. 18 is a plot of intensity against voltage for the device of Example2 as described in this application.

FIG. 19 is a plot of radiance against wavelength for the device ofExample 2 as described in this application.

FIG. 20 is a plot of radiance against wavelength for the device ofExample 4 as described in this application.

FIGS. 21 and 22 are, respectively, plots of brightness and currencyefficiency against voltage for the device of Example 3a as described inthis application.

FIGS. 23 and 24 are plots similar to FIGS. 21 and 22 for the device ofExample 3b as described in this application.

FIGS. 25 and 26 are plots similar to FIGS. 23 and 24 for the device ofExample 3c as described in this application.

FIGS. 27 and 28 are plots similar to FIGS. 25 and 26 for the device ofExample 4a as described in this application.

FIGS. 29 and 30 are plots similar to FIGS. 27 and 28 for the device ofExample 5 as described in this application.

Preferably the complex can also comprise one or more neutral ligandsL_(p) so the complex has the general formula (L_(α))_(n) M₁ M₂ (L_(p)),where L_(p)is a neutral ligand.

There can be more than one group L_(α)and more than one group L_(p) andeach of which group may be the same or different.

M₁ can be any metal ion having an unfilled inner shell which can be usedas the metal and the preferred metals are selected from Sm(III), Eu(II),Eu(III), Tb(III), Dy(III), Yb(III), Lu(III), Gd (III), U(III), U(VI)O₂,Tm(III), Th(IV), Ce (III), Ce(IV), Pr(III), Nd(III), Pm(III), Dy(III),Ho(III), Er(III).

The metal M₂ can be any metal which is not a rare earth, lanthanide oran actinide examples of metals which can be used include lithium,sodium, potassium, rubidium, caesium, beryllium, magnesium, calcium,strontium, barium, copper, silver, gold, zinc, cadmium, boron,aluminium, gallium, indium, germanium, tin, antimony, lead, and metalsof the first, second and third groups of transition metals e.g.manganese, iron, ruthenium, osmium, cobalt, nickel, palladium, platinum,cadmium, chromium, titanium, vanadium, zirconium, tantulum, molybdenum,rhodium, iridium, niobium, scandium, yttrium etc.

The different groups (L_(α)) may be the same or different and can beselected from β diketones such as those of formulae

where R₁, R₂ and R₃ can be the same or different and are selected fromhydrogen, hydrocarbyl groups, substituted and unsubstituted aliphaticgroups substituted and unsubstituted aromatic, heterocyclic andpolycyclic ring structures, fluorocarbons such as trifluoryl methylgroups, halogens such as fluorine or thiophenyl groups; R₁, R₂ and R₃can also be copolymerisable with a monomer e.g. styrene and where X isSe, S or O and Y is hydrogen, hydrocarbyl groups, substituted andunsubstituted aromatic, heterocyclic and polycyclic ring structures,fluorine, fluorocarbons such as trifluoryl methyl groups, halogens suchas fluorine or thiophenyl groups or nitrile.

Examples of R₁ and/or R₂ and/or R₃ include aliphatic, aromatic andheterocyclic alkoxy, aryloxy and carboxy groups, substituted andsubstituted phenyl, fluorophenyl, biphenyl, phenanthrene, anthacene,naphthyl and fluorene groups alkyl groups such as t-butyl, heterocyclicgroups such as carbazole

R₁, R₂ and R₃ can also be

where X is O, S, Se or NH.

A preferred moiety R₁ is trifluoromethyl CF₃ and examples of suchdiketones are, banzoyltrifluoroacetone, p-chlorobenzoyltrifluoroacetone,p-bromotrifluoroacetore, p-phenyltriuoroacetone,1-naphthoyltrifluoroacetone, 2-naphthoyltrifluoroacetone,2-phenathoyltrifluoroacetone, 3-phenanthoyltrifluoroacetone,9-anthroyltrifluoroacetonetrifluoroacetone, cinnamoyltrifluoroacetone,and 2-thenoyltrifluoroacetone.

The different groups (L_(α)) may be the same or different ligands offormulae

where X is O,S; or Se and R₁R₂ and R₃are as above

The different groups (L_(α)) may be the same or different quinolatederivatives such as

where R is hydrocarbyl, aliphatic, aromatic or heterocyclic carboxy,aryloxy, hydroxy or alkoxy e.g. the 8 hydroxy quinolate derivatives or

where R is as above or H or F or

The different groups (L_(α)) may also be the same or differentcarboxylate groups

where R₅ is a substituted or unsubstituted aromatic, polycyclic orheterocyclic ring a polypyridyl group, R₅ can also be a 2-ethyl hexylgroup so L_(α) is 2-ethylhexanoate or R₅ can be a chair structure sothat L_(α) is 2-acetyl cyclohexanoate or L can be

where R₁ and R₂ are as above e.g. alkyl, allenyl, amino or a fused ringsuch as a cyclic or polycyclic ring.

The different groups (L_(α)) may also be

Where R₁ and R₂ are as above.

The groups L_(p) can be selected from

where each Ph which can be the same or different and can be a phenyl(OPNP) or a substituted phenyl group, other substituted or unsubstitutedaromatic group, a substituted or unsubstituted heterocyclic orpolycyclic group, a substituted or unsubstituted fused aromatic groupsuch as a naphthyl, anthracene, phenanthrene, perylene or pyrene group.The substituents can be for example an alkyl, aralkyl, alkoxy, aromatic,heterocyclic, polycyclic group, halogen such as fluorine, cyano, aminoand substituted amino groups etc. Examples are given in FIGS. 1 and 2 ofthe drawings where R, R_(1,) R_(2,) R₃ and R₄ can be the same ordifferent and are selected from hydrogen, hydrocarbyl groups,substituted and unsubstituted aromatic, heterocyclic and polycyclic ringstructures, fluorocarbons such as trifluoryl methyl groups, halogenssuch as fluorine or thiophenyl groups; R, R_(1,) R_(2,) R₃ and R₄ canalso form substituted and unsubstituted fused aromatic, heterocyclic andpolycyclic ring structures and can be copolymerisable with a monomere.g. styrene. R, R_(1,) R_(2,) R₃ and R₄ can also be unsaturatedalkylene groups such as vinyl groups or groups—C—CH₂═CH₂—Rwhere R is as above.

L_(p) can also be compounds of formulae

where R₁, R₂ and R₃ are as referred to above, for example bathophenshown in FIG. 3 of the drawings in which R is as above.

L_(p) can also be

where Ph is as above.

Other examples of L_(p) are as shown in FIGS. 4 to 8

Specific examples of L_(α)and L_(p) are tripyridyl and TUMH, and TMHDcomplexes, α, α′, α″ tripyridyl, crown ethers, cyclans, cryptansphthalocyanans, porphoiyins ethylene diarnine tetramine (EDTA), DCTA,DTPA and TIHA. Where TMHD is 2,2,6,6-tetramethyl-3,5-heptanedionato andOPNP is diphenylphosphonimide triphenyl phosphorane. The formulae of thepolyamines are shown in FIG. 9.

The first electrode is preferably a transparent substrate which is aconductive glass or plastic material which acts as the anode, preferredsubstrates are conductive glasses such as indium tin oxide coated glass,but any glass which is conductive or has a conductive layer can be used.Conductive polymers and conductive polymer coated glass or plasticsmaterials can also be used as the substrate.

The electroluminescent material can be deposited on the substratedirectly by evaporation from a solution of the material in an organicsolvent. The solvent which is used will depend on the material butchlorinated hydrocarbons such as dichloromethane, n-methyl pyrrolidone,dimethyl sulphoxide, tetra hydrofiran dimethylformamide etc. aresuitable in many cases.

Alternatively the material can be deposited by spin coating fromsolution or by vacuum deposition from the solid state e.g. by sputteringor any other conventional method can be used.

The mixed complexes can be made by reacting a mixture of salts of themetals with the organic complexes as in conventional methods of makingthe transition metal complexes.

Examples of complexes of the present invention include Eu(DBM)₃OPNP,Tb(tmhd)₃OPNP, Eu(Zn(DBM)₅OPNP etc.

Optionally there is a layer of an electron transmitting material betweenthe cathode and the electroluminescent material layer, the electrontransmitting material is a material which will transport electrons whenan electric current is passed through electron transmitting materialsinclude a metal complex such as a metal quinolate e.g. an aluminiumquinolate, lithium quinolate a cyano anthracene such as 9,10 dicyanoanthracene, a polystyrene sulphonate and compounds of formulae shown inFIGS. 10 and 11. Instead of being a separate layer the electrontransmitting material can be mixed with the electroluminescent materialand co-deposited with it.

In general the thickness of the layers is from 5 nm to 500 nm.

The second electrode functions as the cathode and can be any low workfunction metal e.g. aluminium, calcium, lithium, silver/magnesium alloysetc., aluminium is a preferred metal. Lithium fluoride can be used asthe second electrode for example by having a lithium fluoride layerformed on a metal.

Preferably there is a hole transporting layer deposited on thetransparent substrate and the electroluminescent material is depositedon the hole transporting layer. The hole transporting layer serves totransport holes and to block the electrons, thus preventing electronsfrom moving into the electrode without recombining with holes. Therecombination of carriers therefore mainly takes place in the emitterlayer.

Hole transporting layers are used in polymer electroluminescent devicesand any of the known hole transporting materials in film form can beused.

In general the thickness of the layers is from 5 nm to 500 nm andpreferably the thickness of the electroluminescent layer is from 20 to50 mn.

The second electrode functions as the cathode and can be any low workfunction metal e.g. aluminium, calcium, lithium, silver/magnesium alloysetc., aluminium is a preferred metal. Lithium fluoride can be used asthe second electrode for example by having a lithium fluoride layerformed on a metal.

Preferably there is a hole transporting layer deposited on thetransparent substrate and the electroluminescent material is depositedon the hole transporting layer. The hole transporting layer serves totransport holes and to block the electrons, thus preventing electronsfrom moving into the electrode without recombining with holes. Therecombination of carriers therefore mainly takes place in the emitterlayer.

Preferably there is a hole transporting layer deposited on thetransparent substrate and the electroluminescent material is depositedon the hole transporting layer. The hole transporting layer serves totransport holes and to block the electrons, thus preventing electronsfrom moving into the electrode without recombining with holes. Therecombination of carriers therefore mainly takes place in the emitterlayer.

Hole transporting layers are used in polymer electroluminescent devicesand any of the known hole transporting materials in film form can beused.

Examples of such hole transporting materials are aromatic aminecomplexes such as poly (vinylcarbazole),N,N′-diphenyl-N,N′-bis(3-methylphenyl)-1,1′-biphenyl-4,4′-diamine (TPD), anunsubstituted or substituted polymer of an amino substituted aromaticcompound, a polyaniline, substituted polyanilines, polythiophenes,substituted polythiophenes, polysilanes etc. Examples of polyanilinesare polymers of

where R is in the ortho—or meta-position and is hydrogen, C1–18 alkyl,C1–6 alkoxy, amino, chloro, bromo, hydroxy or the group

where R is ally or aryl and R′ is hydrogen, C1–6 alkyl or aryl with atleast one other monomer of formula I above.

Polyanilines which can be used in the present invention have the generalformula

where p is from 1 to 10 and n is from 1 to 20, R is as defined above andX is an anion, preferably selected from Cl, Br, SO₄, BF₄, PF₆, H₂PO₃,H₂PO₄, arylsulphonate, arenedicarboxylate, polystyrenesulphonate,polyacrylate alkysulphonate, vinylsulphonate, vinylbenzene sulphonate,cellulose sulphonate, camphor sulphonates, cellulose sulphate or aperfluorinated polyanion.

Examples of arylsulphonates are p-toluenesulphonate, benzenesulphonate,9,10-anthraquinone-sulphonate and anthracenesulphonate, an example of anarenedicarboxylate is phthalate and an example of arenecarboxylate isbenzoate.

We have found that protonated polymers of the unsubstituted orsubstituted polymer of an amino substituted aromatic compound such as apolyaniline are difficult to evaporate or cannot be evaporated, howeverwe have surprisingly found that if the unsubstituted or substitutedpolymer of an amino substituted aromatic compound is deprotonated the itcan be easily evaporated i.e. the polymer is evaporable.

Preferably evaporable deprotonated polymers of unsubstituted orsubstituted polymer of an amino substituted aromatic compound are used.The de-protonated unsubstituted or substituted polymer of an aminosubstituted aromatic compound can be formed by deprotonating the polymerby treatment with an alkali such as ammonium hydroxide or an alkalimetal hydroxide such as sodium hydroxide or potassium hydroxide.

The degree of protonation can be controlled by forming a protonatedpolyaniline and de-protonating. Methods of preparing polyanilines aredescribed in the article by A. G. MacDiarmid and A. F. Epstein, FaradayDiscussions, Chem Soc. 88 P319 1989.

The conductivity of the polyaniline is dependant on the degree ofprotonation with the maximum conductivity being when the degree ofprotonation is between 40 and 60% e.g. about 50% for example.

Preferably the polymer is substantially fully deprotonated

A polyaniline can be formed of octamer units i.e. p is four e.g.

The polyanilines can have conductivities of the order of 1×10⁻¹ Siemencm⁻¹ or higher.

The aromatic rings can be unsubstituted or substituted e.g. by a C1 to20 alkyl group such as ethyl.

The polyaniline can be a copolymer of aniline and preferred copolymersare the copolymers of aniline with o-anisidine, m-sulphanilic acid oro-aminophenol, or o-toluidine with o-aminophenol, o-ethylamine,o-phenylene diamine or with amino anthracenes.

Other polymers of an amino substituted aromatic compound which can beused include substituted or unsubstituted polyaminonapthalenes,polyaminoanthracenes, polyaminophenanthrenes, etc. and polymers of anyother condensed polyaromatic compound. Polyaminoanthracenes and methodsof making them are disclosed in U.S. Pat. No. 6,153,726. The aromaticrings can be unsubstituted or substituted e.g. by a group R as definedabove.

The polyanilines can be deposited on the first electrode by conventionalmethods e.g. by vacuum evaporation, spin coating, chemical deposition,direct electrodeposition etc. preferably the thickness of thepolyaniline layer is such that the layer is conductive and transparentand can is preferably from 20 nm to 200 nm. The polyanilines can bedoped or undoped, when they are doped they can be dissolved in a solventand deposited as a film, when they are undoped they are solids and canbe deposited by vacuum evaporation i.e. by sublimation.

The polymers of an amino substituted aromatic compound such aspolyanilines referred to above can also be used as buffer layers with orin conjunction with other hole transporting materials.

The structural formulae of some other hole transporting materials areshown in FIGS. 12 to 16 of the drawings, where R_(1,) R₂ and R₃ can bethe same or different and are selected from hydrogen, and substitutedand unsubstituted hydrocarbyl groups such as substituted andunsubstituted aliphatic groups, substituted and unsubstituted aromatic,heterocyclic and polycyclic ring structures, fluorocarbons such astrifluoryl methyl groups, halogens such as fluorine or thiophenylgroups; R_(1,) R₂ and R₃ can also form substituted and unsubstitutedfused aromatic, heterocyclic and polycyclic ring structures and can becopolymerisable with a monomer e.g. styrene. X is Se, S or O, Y can behydrogen, substituted or unsubstituted hydrocarbyl groups, such assubstituted and unsubstituted aromatic, heterocyclic and polycyclic ringstructures, fluorine, fluorocarbons such as trifluoryl methyl groups,halogens such as fluorine or thiophenyl groups or nitrile.

Examples of R₁ and/or R₂ and/or R₃ include aliphatic, aromatic andheterocyclic alkoxy, aryloxy and carboxy groups, substituted andsubstituted phenyl, fluorophenyl, biphenyl, phenanthrene, anthracene,naphthyl and fluorene groups alkyl groups such as t-butyl, heterocyclicgroups such as carbazole.

The preparation of complexes according to the invention are illustratedin the following examples.

EXAMPLE 1 Preparation of EuZn(DBM)₅(OPNP)

A mixture of dibenzoylmethane (DBM) (4.1 g; 0.0 18 mole) and OPNP (3.5g; 0.007 mole) was dissolved in ethanol (40 ml) by warming themagnetically stirred solution. A solution containing ZnCl₂ (0.5 g;0.0037 mole) and EuCl₃ (1.34 g; 0.0037 mole) in water (10 ml) was addedto the reaction mixture, followed by 2N NaOH solution until the pH was6–7. The precipitate was filtered off, washed with water and ethanol anddried under vacuum at 80° C. for 16 hours. The product had a M.P. of182° C. Films of the product were obtained by dissolving the product ina solvent and evaporating from the solution.

Elemental analysis: Found C 69.59, H 4.56, N 0.79. C₁₀₅H₈₀O₁₁NP₂EuZnrequires C 69.63, H 4.45 and N 0.77. The elemental analysis suggeststhat there was only one OPNP.

The ultraviolet spectrum was

UV (λmax) nm (thick evaporated film): 356, 196

UV (λmax) nm (thin evaporated film): 362

UV (λmax) nm (thin film made from CH₂Cl₂ solution): 360, 195

TGA: ° C. (% weight loss): 350(11),444 (39) and 555 (80)

The photoluminescent colour had co-ordinates: x 0.66, y 0.33

EXAMPLE 2 EuAl(DBM)₆OPNP

A warm ethanolic solution (50 ml) of dibenzoylmethane (DBM) (3.67 g.0.016 mole) was mixed with an ethanolic solution (30 ml) of OPNP (2.60g. 0.005 mole). NaOH (0.65 g, 0.0 16 mole) in water (30 ml) was added tothe ligand (DBM) solution while stirring. The solution became darkyellow. The solution was stirred for 10 minutes. After 10 minutes, amixture of EuCl₃.6H₂O (1 g 0.0027 mole) in ethanol: water (1:1) (20 ml)and AlCl₃.6H₂O (0.658 g. 0.0027 mole) in water (20 ml) was slowly addedwhile stirring. The reaction mixture was stirred for 5 hours at 60° C.The yellow colour product was suction filtered and thoroughly washedwith water followed by ethanol. Product was vacuum dried at 80° C.Analysis showed it to be EuAL(DBM)₆OPNP.

EXAMPLE 3 Electroluminescent Device

An ITO coated glass piece (1×1 cm² ) had a portion etched out withconcentrated hydrochloric acid to remove the ITO and was cleaned anddried. The device is shown in FIG. 17 where (1) is ITO; (2) CuPc; (3)α-NPB; (4) EuZn(DBM)₅(OPNP); (5) BCP; (6) Alq_(3;) (7) LiF; (8) Al wasfabricated by sequentially forming on the ITO, by vacuum evaporation,layers comprising:

ITO(100Ω/sqr)|CuPc (6.6 nm)|α-NPB(35 mm)|EuZn(DBM)₅(OPNP)(35 nm)|BCP (8nm)|Alq₃(10 nm)|LiF(3 nm)|Al (500 nm).

Where CuPc is copper phthalocyanine, BCP bathocupron and Alq₃ isaluminiumn quinolate.

The EuZn(DBM)₅(OPNP) was prepared as in Example 1.

The organic coating on the portion which had been etched with theconcentrated hydrochloric acid was wiped with a cotton bud.

The coated electrodes were stored in a vacuum desiccator over amolecular sieve and phosphorous pentoxide until they were loaded into avacuum coater (Edwards, 10⁻⁶ torr) and aluminium top contacts made. Theactive area of the LED's was 0.08 cm by 0.1 cm² the devices were thenkept in a vacuum desiccator until the electroluminescent studies wereperformed.

The ITO electrode was always connected to the positive terminal. Thecurrent vs. voltage studies were carried out on a computer controlledKeithly 2400 source meter.

An electric current was applied across the device and a plot of theradiance and intensity against voltage is shown in the graph of FIG. 18.

A plot of radiance against wavelength is shown in FIG. 19, and thecolour coordinates according to the CIE colour chart were x=0.65857;y=0.33356 which is reddish orange.

EXAMPLE 3a

Other devices were fabricated as above with the structure 100ΩITO and Alelectrodes

Material CuPc α-NPB EuZn(DBM)₅(OPNP) BCP Alq₃ LiF Thickness/ 1.4 6.936.3 4.0 11.5 0.8 nm

The electroluminescent properties were

Current Current Voltage/ Current/ Density/ Brightness/ Efficiency/Electroluminescent V mA mAcm⁻² x, y cdm⁻² cdA⁻¹ Efficiency/lmW⁻¹ 19.010.10 168.33 0.55, 0.42 160.60 0.10 0.02

The results are shown graphically in FIGS. 21 and 22

EXAMPLE 3b

Other devices were fabricated as above with the structure 100Ω ITO andAl electrodes

Material CuPc α-NPB EuZn(DBM)₅(OPNP) BCP Alq₃ LiF Thickness/ 4.2 20.2117.9 4.0 11.5 0.8 nm

The electroluminescent properties were

Current Current Voltage/ Current/ Density/ Brightness/ Efficiency/Electroluminescent V mA mAcm⁻² x, y cdm⁻² cdA⁻ Efficiency/ImW⁻¹ 22.01.21 20.17 0.62, 0.37 53.78 0.27 0.040

The results are shown graphically in FIGS. 23 and 24

EXAMPLE 3c

Other devices were fabricated as above with the structure 47Ω ITO and Alelectrodes

Material CuPc β-NPB EuZn(DBM)₅(OPNP) BCP Alq₃ LiF Thickness/ 2.0 8.555.0 6.0 17.0 0.9 nm

The electroluminescent properties were

Current Current Voltage/ Current/ Density/ Brightness/ Efficiency/Electroluminescent V mA mAcm⁻² x, y cdm⁻² cdA⁻¹ Efficiency/ImW⁻¹ 16.00.81 13.60 0.59, 0.40 29.74 0.22 0.043

The results are shown graphically in FIGS. 25 and 26

EXAMPLE 4 Electroluminescent Device

Example 3 was repeated using EuAl(DBM)₆OPNP prepared as in Example 2 andthe plot of radiance against wavelength is shown in FIG. 20 and thecolour coordinates according to the CIE colour chart were x=0.60622;y=0.3224 which is reddish orange.

EXAMPLE 4a

Other devices were fabricated as above with the structure 100Ω ITO andAl electrodes

Material CuPc α-NPB EuA1(DBM)₆OPNP BCP Alq₃ LiF Thickness/ 2.2 18.3 55.06.0 12.0 0.9 nm

The electroluminescent properties were

Current Current Voltage/ Current/ Density/ Brightness/ Efficiency/Electroluminescent V mA mAcm⁻² x, y cdm⁻² cdA⁻¹ Efficiency/ImW⁻¹ 21.03.60 60.0 0.43, 0.42 528.0 0.132 0.0880

The results are shown graphically in FIGS. 27 and 28

EXAMPLE 5

Example 4 was repeated using EuSc(DBM)₆OPNP 47Ω ITO and Al electrodes

Material CuPc α-NPB EuSc(DBM)₆OPNP BCP Alq₃ LiF Thickness 2.1 8.5 54.96.0 17.5 1.0 nm

The electroluminescent properties were

Current Current Voltage/ Current/ Density/ Brightness/ Efficiency/Electroluminescent V mA mAcm⁻² x, y cdm⁻² cdA⁻¹ Efficiency/ImW⁻¹ 22.03.60 60.0 0.38, 0.37 43.79 0.73 1.04 × 10⁻²

The results are shown graphically in FIGS. 29 and 30.

1. An electroluminescent device comprising: (i) a first electrode; (ii)a second electrode: and, (iii) a layer of an electroluminescent materialpositioned between said first and second electrodes, wherein saidelectroluminescent material is selected from the group consisting ofmaterials having the general chemical formula (L_(α))_(n)M₁M₂ andmaterials having the general chemical formula (L_(α))_(n)M₁M₂(L_(p))wherein: M₁ is selected from the group consisting of Sm(III), Eu(II),Eu(III), Tb(III), Dy(III), Yb(III), Lu(III), Gd(III), Tm(III), Th(IV),Ce(III), Ce(IV), Pr(III), Nd(III), Pm(III), Dy(III), Ho(III) or Er(III);M₂ is selected from the group consisting of lithium, sodium, potassium,rubidium, caesium, magnesium, calcium, strontium, barium, boron,aluminum, gallium, indium, germanium, tin, lead, scandium, titanium,vanadium, chromium, nickel, copper, zinc, yttrium, zirconium, niobium,molybdenum, ruthenium, rhodium, palladium, silver, cadmium, tantalum,osmium, iridium, platinum and gold; n is an integer equal to thecombined valence state of M₁ and M₂; L_(α)is selected from the group ofmaterials consisting of (a) to (f) as follows:

 wherein R₁ and R₂ can be the same or different and are independentlyselected from the group consisting of hydrogen; substituted orunsubstituted aliphatic groups; substituted or unsubstituted aromatic,heterocyclic or polycyclic ring structures; fluorocarbon groups; andhalogens; X is selected from the group consisting of Se, S, and O; and,Y is selected from the group consisting of hydrogen; substituted orunsubstituted aliphatic groups; substituted or unsubstituted aromatic,heterocyclic or polycyclic ring structures; fluorocarbon groups;halogens; and nitrile;

 wherein R is selected from the group consisting of hydrocarbyl groups,aliphatic groups, aromatic groups, heterocyclic groups, carboxy groups,aryloxy groups, hydroxy groups and alkoxy groups;

 wherein R₅ is selected from the group consisting of substituted orunsubstituted aromatic groups, heterocyclic groups and polycyclic rings;

 wherein R₁ and R₂ are as defined in (a) above;

 wherein R₁ and R₂ are as defined in (a) above; and,

 wherein R is selected from the group consisting of hydrocarbyl groups,aliphatic groups, aromatic groups, heterocyclic groups, carboxy groups,aryloxy groups, hydroxyl groups and alkoxy groups; and, Lp is selectedfrom the group of materials consisting of (g) to (jj) as follows:

 wherein each Ph group can be the same or different and areindependently selected from the group consisting of substituted orunsubstituted aromatic groups and substituted or unsubstitutedheterocyclic or polycyclic groups with substituents selected from alkyl,aralkyl, alkoxy, aromatic, heterocyclic, and polycyclic groups,halogens, cyano groups, and substituted or unsubstituted amino groups;and, Z is selected from O and S;

 wherein R₁, R₂ and R₃ can be the same or different and areindependently selected from the group consisting of hydrogen;substituted or unsubstituted aliphatic groups; substituted andunsubstituted aromatic, heterocyclic and polycyclic ring structures;fluorocarbon groups and halogens;

 wherein R is selected from the group consisting of hydrocarbyl groups,aliphatic groups, aromatic groups, heterocyclic groups, carboxy groups,aryloxy groups, hydroxyl groups and alkoxy groups.
 2. Theelectroluminescent device according to claim 1 wherein theelectroluminescent material comprises EuZn(DBM)₅OPNP.
 3. Theelectroluminescent device according to claim 1 wherein theelectroluminescent material comprises EuAl(DBM)₆OPNP.
 4. Theelectroluminescent device according to claim 1 wherein theelectroluminescent material comprises EuSc(DBM)₆OPNP.
 5. Theelectroluminescent device according to claim 1 wherein a layer of a holetransmitting material is positioned between the first electrode and thelayer of the electroluminescent material.
 6. The electroluminescentdevice according to claim 5 wherein the hole transmitting layer isformed from a material selected from the group consisting ofpoly(vinylcarbazole),N,N′-diphenyl-N,N′-bis(3-methylphenyl)-1,1′-biphenyl-4,4′diamine (TPD),polyaniline, and a substituted polyaniline.
 7. The electroluminescentdevice according to claim 1 wherein a layer of an electron transmittingmaterial is positioned between the second electrode and the layer ofelectroluminescent material.
 8. The electroluminescent device accordingto claim 7 wherein the electron transmitting material is a metalquinolate.
 9. The electroluminescent device according to claim 8 whereinthe metal quinolate is selected from the group consisting of lithiumquinolate, sodium quinolate, potassium quinolate, zinc quinolate,magnesium quinolate and aluminum quinolate.
 10. The electroluminescentdevice according to claim 1 wherein a layer of a hole transmittingmaterial is positioned between the first electrode and the layer of theelectroluminescent material, and further wherein a layer of an electrontransmitting material is positioned between the second electrode and thelayer of electroluminescent material.
 11. The electroluminescent deviceaccording to claim 10 wherein the hole transmitting layer comprises acopper phthalocyanine layer and the electron transmitting layercomprises lithium fluoride.